Manolis J. Manos

A new ammonium–thiourea intercalated layered metal sulfide (T-AMS-1), synthesized by the thiourea flux route, exhibits highly efficient Pb ²⁺ and Cr ⁶⁺ sorption properties and reusability under continuous flow conditions.

With terrestrial uranium reserves declining, the vast amount of uranium in seawater represents an indispensable, sustainable resource. Exploiting this reservoir not only advances the remediation of aquatic environments from toxic metals but also secures the long-term nuclear fuel supply. Here, we report the synthesis and characterization of a robust UiO-66-type metal–organic framework with the formula [Zr6O4(OH)6.6(MTATP)4.7(H2O)2.6]·solvents (MOR-4, metal–organic resin-4), where H2MTATP = 2-((3-(methyl-thio)propyl)amino)terephthalic acid, featuring defective Zr6 clusters interconnected by amino/thioether-functionalized ligands. Batch sorption studies show rapid and efficient removal of uranyl ions (UO22+) under acidic and neutral conditions, achieving equilibrium within minutes and reducing uranium concentrations to <2 ppb, well below the World Health Organization’s drinking water threshold (30 ppb). The sorbent exhibits high selectivity for uranium in the presence of competing ions, with a modest reduction in performance observed under carbonate-rich conditions. The excellent sorption properties of the MOF are due to the strong binding of uranyl cations to the MOF’s defect sites, as revealed by a series of experimental data. Most notably, the sorbent successfully extracts uranium from mildly acidified seawater samples, demonstrating its remarkable selectivity under high-competition conditions. For practical applications, a column packed with MOR-4/Calcium Alginate beads and silica sand was used to remove and recover uranium from the acidified seawater under continuous-flow conditions. The results exceeded expectations, revealing U removal and recovery above 95% and 85%, respectively, across two sorption/desorption cycles, indicating the strong potential of the material for uranium sequestration from seawater. Furthermore, treating MOR-4 with either a strong acid (pH ∼ 0) or a base (pH ∼ 12) resulted in materials with increased defects and larger pore sizes than those of the pristine material, providing a route to isolate materials with enhanced properties.

This study reports on the synthesis, structural characterization and gas sorption studies of a homometallic 2D Cd²⁺ MOF and two heterometallic 3D Cd²⁺/Ca²⁺ and Cd²⁺/Sr²⁺ -MOFs based on the angular tetracarboxylic ligand 3,3′,4,4′-sulfonyltetracarboxylic acid (H₄STBA). The homometallic 2D Cd²⁺ MOF with the formula [NH₂(CH₃)₂]⁺₂[Cd(STBA)]²⁻_n·nDMF·1.5nH₂O—(1)_n·nDMF·1.5nH₂O was synthesized from the reaction of CdCl₂·H₂O and 3,3′,4,4′-diphthalic sulfonyl dianhydride (3,3′,4,4′-DPSDA) with stoichiometric ratio of 1:1.3 in DMF/H₂O (5/2 mL) at 100 °C. The two heterometallic Cd²⁺/Ca²⁺ and Cd²⁺/Sr²⁺ compounds were prepared from analogous reactions to this afforded (1)_n·nDMF·1.5nH₂O with the difference that the reaction mixture also contained AE(NO₃)₂ (AE²⁺ = Ca²⁺ or Sr²⁺) and, in particular, from the reaction of AE(NO₃)₂, CdCl₂·H₂O and 3,3′,4,4′-DPSDA with stoichiometric ratio 1:1.1:1.4 in DMF/H₂O (5/2 mL) at 100 °C. Notably, compounds [CdCa(STBA)(H₂O)₂]_n·0.5nDMF—(2)_n·0.5nDMF and [CdSr(STBA)(H₂O)₂]_n·0.5nDMF—(3)_n·0.5nDMF are the first heterometallic compounds Mⁿ⁺/AE²⁺ (M = any metal ion) reported containing ligand H₄STBA. The structure of (1)_n·nDMF·1.5nH₂O comprises a 2D network based on helical 1D chain secondary building unit (SBU) [Cd²⁺(STBA)⁴⁻)]²⁻. The 2D sheets are linked through hydrogen bonding interactions, giving rise to a pseudo-3D structure. On the other hand, compounds (2)_n·1.5nH₂O and (3)_n·1.5nH₂O display 3D microporous structures consisting of a helical 1D chain SBU [Cd²⁺AE²⁺(STBA)⁴⁻)]. All three compounds contain rhombic channels along c axes. The three MOFs exhibit an appreciable thermal stability, up to 350–400 °C. Gas sorption measurements on activated materials (2)_n and (3)_n revealed moderate BET surface areas of 370 m²/g and 343 m²/g, respectively, along with CO₂ uptake capacity of 2.58 mmol/g at 273 K.

The steadily increasing use of gold and the limited gold reserves have instigated a significant research effort to develop materials with efficient gold recovery. However, most works focus only on the uptake of Au ions, ignoring Au nanoparticles, which are increasingly used in various applications and represent a critical source of Au. Furthermore, the reported gold recovery studies involve powder-form materials that cannot be easily retrieved after the sorption process, thus making them unattractive for real, large-scale applications. The present work reports a Zr-(IV) metal-organic framework (MOF) with a defective microporous structure and amino-thiophene functional groups, which exhibit strong interactions with Au species. The MOF was immobilized on cotton fabric via an in situ method to create an easily retrievable bulk sorbent composite, which was investigated in detail for its sorption properties toward Au ions and Au nanoparticles (AuNPs). The immobilized sorbent showed relatively fast sorption kinetics (85%) of gold either as ions or AuNPs from genuine water samples. The latter property allowed the use of the MOF-fabric sorbent for the development of the first passive sampling sorbent phase for the long-term monitoring or recovery of AuNPs from natural waters. Notably, the sorbent was highly effective for the selective recovery of Au (∼97%) from an electronic waste simulant under flow conditions. The reusability of the MOF, in a composite form with calcium alginate, as Au sorbent was demonstrated under flow conditions for several cycles, indicating the potential of the material for Au separation applications. Overall, the reported sorbent offers a practical and cost-effective means for efficiently recovering ionic and nanoparticle Au species from complex water and wastewater media.

Ultramicroporous and acid-resistant multivariate Al( iii ) metal–organic frameworks (MOFs) are reported, demonstrating selective CO ₂ adsorption properties and highly efficient uptake of dichromate.

New Ce( iv ) MOFs demonstrate highly efficient Pb ²⁺ sorption properties and excellent reusability for Pb ²⁺ capture under continuous flow conditions.

Lead is a toxic heavy metal that pollutes the environment and accumulates in the human body, causing many severe health issues. Metal sulfides have emerged as promising sorbents for rapidly decontaminating Pb²⁺-containing wastewater, showing exceptional sorption kinetics, capacities, and selectivity against common competitive ionic species. In this study, we present modified SnS₂ phases, namely, SnS₂(DMA)_0.7(H₂O)_0.3 (SnS₂/DMA, DMA = dimethylamine) and Sn_1-xS₂·yH₂O (SnS₂/acid), which demonstrated efficient removal of Pb²⁺ ions from aqueous solutions. Both materials exhibited fast kinetics (≤4 min), high sorption capacities (838.0 mg g^-1 for SnS₂/DMA and 190.0 mg g^-1 for SnS₂/acid), remarkable selectivity toward Pb²⁺ over several competing cations and in various pH values, because of strong Pb-S covalent interactions. Aiming for practical wastewater treatment, we immobilized SnS₂/DMA and SnS₂/acid on cotton fabrics, marking this as the initial application of metal sulfides immobilized onto cotton substrates. The metal sulfide-fabric composites were utilized to remove Pb²⁺ under continuous flow conditions, showing significant Pb²⁺ sorption properties. Significantly, the metal sulfide-based composites can be regenerated and reused over several Pb²⁺ sorption cycles. This feature, demonstrated for the first time in metal sulfide materials, constitutes a breakthrough for this class of sorbents.

This work demonstrates that the packaging material commonly called “bubble wraps” (Aeroplast) can be leveraged to serve as a probe to visible sunlight exposure. This probe relies on a newly developed layered metal selenide photocatalyst with the general formula (DMAH)_2xMn_xSn_3–xSe₆ (DMSe‐1) (x = 1.3–1.7; DMAH⁺ = dimethylammonium), featuring a narrow bandgap of 0.76 eV, in addition to an indicator dye and a reducing agent. The photochemically sensitive probe is introduced into the air‐filled compartments of bubble wraps and undergoes photocatalytic degradation, resulting in a chromatic response to sunlight exposure. The probe's sensitivity to variable irradiation doses can be adjusted by varying the amount of the photocatalyst. The color intensity correlates with the absorbed irradiation dose, allowing for qualitative assessment by the naked eye or quantitative measurement using the RGB color system. The results obtained from the new probe agree with those obtained from standard sunlight pyranometers (r = 0.98), with an average error of <15%. This suggests that beyond their use as protective coatings, bubble wraps can be successfully repurposed as visible light sensors. Furthermore, this study describes the initial use of metal chalcogenides as visible light probes, potentially paving the way for the development of innovative light‐sensitive materials.